Propeller sizes

[jimi]

Why do all the power boats I see have such teensy weensy propellers .. would'nt you go much faster if you had proper ones?

<hr width=100% size=1>.. when's that again, but ..

 

[Bejasus]

Aye, but then they'd huv tae hae muckle great suck, squeeze, bang & blow thingies.

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[paulineb]

sounds like the ideal wife h00

<hr width=100% size=1>Pxx

<A target="_blank" HREF=http://www.paulinebeddoes.co.uk/php-cgi/gallery2>Perils of Pauline in Pics</A>

 

[Bejasus]

lol.../forums/images/icons/wink.gif

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[MainlySteam]

Or, why can't we raggies go much faster than them with our great big proper ones???

John

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[Talbot]

very simple. Raggies are better with larger props cause they work better at slow speeds than the small wizzy things required for stinkies. Look at the differences on outboards between the 9hp designed for a tender, and that designed to work as a sail drive. The sail drive is designed for thrust rather than speed. The downside of course is that the larger props cause more resistance when sailing, thus the design of folding props.

The main requirement for sailing boats is to minimise the cavitation caused by the propellor, and thus move as much water backwards as possible. This requirement is best met by turning a large prop slowly.



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[MainlySteam]

But my dinghy has a small whizzy propellor and it is slower than my yacht which has a big whirly propellor? So the theory doesn't hold up does it?

My dinghy's outboard propellor is about 5 inches in diameter and my yacht's propellor is 18 inches in dia so that should mean my dinghy will go 3.6 times as fast whereas it goes about half as fast?

Anyway it is happy New Year to all on the 2003 side of the sun from the 2004 side.

John

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[ccscott49]

Oooooooo! you are naughty!...............But I like You!

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[Gtdog]

Next up on the list is the HP and torque of the engine, and then the weight of the boat, and if you are lucky the service speed requirements.
Big math required but I am sure that you will be able to find someone to help!

<hr width=100% size=1>Work? You call this Work?

 

[BrendanS]

I wanted one like they have on nuclear subs. Apart from the fact they look wicked, I'd be able to creep silently up on raggies before hitting them with my wash

<hr width=100% size=1> I asked an economist for her phone number....and she gave me an estimate

 

[Gtdog]

Variable pitch too!
Wow just think, all of your engines torque all of the time!
Now I saw one lying about 62nm south of the Needles... Hmm where is my hacksaw?

<hr width=100% size=1>Work? You call this Work?